The ATOMKI laboratory in Debrecen, Hungary claimed to have found evidence of a new fundamental particle with a mass of about 17 MeV in the details of several different radioactive decays.
The MEGII detector looked for the claimed X17 particle in a dedicated experiment to search for it.
It didn't find it and set strict limits on the properties it would have had to have had to evade detection in this experiment. The introduction to the paper also notes that explanations for the anomaly observed involving "Standard Model or nuclear physics effects unaccounted for previously have also been suggested."
2 comments:
that was fast :)
We present in this paper the analysis of a four-week data-taking in 2023 with a beam energy of 1080 keV
5 Conclusions
A search for the hypothetical X17 particle suggested to
explain an anomaly first observed at an experiment in
ATOMKI was conducted with the MEG II apparatus at PSI.
The e+e− pair production in the nuclear transitions of both
17.6 MeV and 18.1 MeV 8Be excited states produced in the
nuclear interaction of protons with 7Li was studied. In our
dataset, 8Be∗(18.1) → 8Be + e+e− represents 21.6(25)% of
all IPC transitions to ground state
10
X17 masses between 16.5 MeV/c2 and 17.1 MeV/c2. The
Atomki X17 hypothesis was tested and a 6.2% (1.5σ ) p-
value was obtained. Improved sensitivity to the particle pro-
duction can be achieved with higher statistics to be collected
at the 1030 keV resonance.
this is bad news for x17 but 1.5σ isn't much and MEG II data from 1 month of data points and their plans for 2025 is over at the 1030 keV resonance.
more of a testing run
PADME and Montreal results to be published
from the paper
We present in this paper the analysis of a four-week data-taking in 2023 with a beam energy of 1080 keV
This dataset is also compared to the February 2023
Eb = 1080 keV data.
4 Branching ratio results
Figure 8 shows the result of the fit to the full 2023 data sam-
ple, reconstructed and selected as detailed above. The sum
of the background contributions well describes the data. A
goodness-of-fit test, based on the Poisson log-likelihood chi-
square statistics defined in [25], returns a p-value of 10.5 %
by randomly generating a set of pseudo-experiments, indi-
cating no significant deviation from the underlying model.
The best fit estimates 12.6(9) % (45.8(13) %) of the
IPC events coming from the 18.1 MeV (17.6 MeV) reso-
nance de-exciting to ground state and zero events from the
17.9 MeV IPC. The best fit of the signal is obtained at
mX17 = 16.5 MeV/c2, with 10 events from the 18.1 MeV
resonance and with 0 from the 17.6 MeV resonance.
We build confidence regions in the three-dimensional
parameter space (R17.6, R18.1, mX17), adopting the Feldman-
they imply that with 10 events from the 18.1 MeV
resonance
not statistically significant but maybe MEGII detector looked for the claimed X17 particle and discover x18.1 particle instead with 10 events from the 18.1 MeV
resonance?
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